Synthetic esters such as polyol esters and adipates, low viscosity poly alpha olefins (PAO) such as PAO 2, and vegetable oils such as canola oil and oleates have been described for use industrially as biodegradable base stocks to formulate lubricants. Such base stocks may be used in the production of lubricating oils for automotives, industrial lubricants, and lubricating greases. Finished lubricants typically comprise the base oil and additives to help achieve desired viscometric properties, low temperature behavior, oxidative stability, corrosion protection, demulsibility and water rejection, friction coefficients, lubricities, wear protection, air release, color and other properties. However, it is generally understood that biodegradability cannot be improved by using common additives that are available in today's marketplace. For environmental, economical, and regulatory reasons, it is of interest to produce biodegradable lubricating oils, other biodegradable lubricants, and compositions including lubricating oils and/or lubricants, from renewable sources of biological origin.
Estolides present a potential source of biobased, biodegradable oils that may be useful as lubricants and base stocks. Several estolide synthetic processes have been previously described, such as the homopolymerization of castor oil fatty acids or 12-hydroxystearic acid under thermal or acid catalyzed conditions, as well as the production of estolides from unsaturated fatty acids using a high temperature and pressure condensation over clay catalysts. Processes for the enzymatic production of estolides from hydroxy fatty acids present in castor oil using lipase have also been described.
In U.S. Pat. No. 6,018,063, Isbell et al. described estolide compounds derived from oleic acids under acidic conditions and having properties for use as lubricant base stocks, wherein the “capping” fatty acid comprises oleic or stearic acid. In U.S. Pat. No. 6,316,649, Cermak et al. reported estolides derived from oleic acids and having capping materials derived from C6 to C14 fatty acids. According to Cermak et al., larger capping materials such as stearic acid adversely affect the properties of the estolide, such that having a greater percentage of stearic acid as the capping moiety generally increases pour point temperatures.